A People's Daily article said Ryukyus were a “vassal state” of China before Japan annexed the islands

China has dismissed a diplomatic protest by Japan over a commentary in a state-run publication that challenged Tokyo's ownership of Okinawa, home to major US bases.

The latest angry exchange could further strain tense relations between Asia's two largest economies, which are involved in a stand-off over a group of uninhabited islands in the East China Sea, called the Senkakus in Japan and the Diaoyus in China.

The People's Daily, the Chinese Communist Party's mouthpiece, published a commentary on Wednesday, which said ownership of the Ryukyu islands - of which Okinawa is the biggest - should be re-examined, prompting Japan to lodge the diplomatic protest.

"The relevant scholars' academic articles reflect attention and research paid by China's populace and academia to the Diaoyu Islands and related historical problems," Hua said.

Japan's Chief Cabinet Secretary Yoshihide Suga said the islands were Japanese territory.

"Japan lodged a stern protest that we can by no means accept the article in question if it reflects the Chinese government's stance," Suga said.

In the commentary, the scholars, Zhang Haipeng and Li Guoqiang from a top government think tank, the Chinese Academy of Social Sciences, called the Ryukyu Islands a "vassal state" of China's Ming (1368-1644) and Qing (1644-1911) dynasties before they were annexed by Japan, suggesting China had a historical claim to the island chain.

"Hanging in the balance of history, the unresolved problem of the Ryukyus has finally arrived at the time for reconsideration," the scholars wrote.

Analysts in Japan have branded China's efforts to assert sovereignty over the scattered islands of the Ryukyus as "ridiculous" - but equally warned that the claim may be Beijing's opening move to seize the Diaoyus.

"I see this as a tactical move by the Chinese Communist Party, but I do believe that China is seeking to capture the Okinawan islands in the future," said Yoichi Shimada, a professor of international relations at Fukui Prefectural University.

"It might be difficult for them to invade the main island - that is not a realistic aim because the US Marines are stationed there - but this is part of their plan to take the Senkakus, then some of the more remote islands," he said.

Okinawa hosts most of the 50,000 US troops in Japan.

Go Ito, a professor of international relations at Tokyo's Meiji University, agrees Beijing's claim to the territory is "quite simply ridiculous". "If Italy applied the same logic, it could claim that pretty much all of Europe is sovereign Italian territory because it was once under the control of the Roman Empire," he said.

It was not the first time mainland media had challenged Japan's sovereignty over the Ryukyus from a historical perspective. Last week, World Affairs, a Foreign Ministry semi-monthly, published a similar commentary written by Fudan University professor Lei Yuhong.

It said that according to the Okinawa Reversion Treaty signed between Washington and Tokyo in 1971, the US only handed administrative rights over Okinawa to Japan, not its sovereignty. Mainland-based experts said the point raised in the two articles was targeting the US.

Professor Wang Hanling, a maritime expert at the Chinese Academy of Social Sciences, said Beijing had no intention of taking over Okinawa, "but those articles carried by official media show that we cannot tolerate what Japan and the US have done to us recently".

He said the Pentagon's reiteration of Japan's administrative rights over the Diaoyus in its latest report on China had also made Beijing unhappy.

Zhou Yongsheng, an expert on Japan affairs at China Foreign Affairs University, said the articles indicated that some historians were trying to push Japan back to the negotiating table.

This article appeared in the South China Morning Post print edition as China brushes off Japan's protest over Okinawa China brushes off Japan's protest